Аннотация
We present spectroscopic follow-up observations of CR7 with ALMA, targeted at
constraining the infrared (IR) continuum and CII$_158 m$
line-emission at high spatial resolution matched to the HST/WFC3 imaging. CR7
is a luminous Ly$\alpha$ emitting galaxy at $z=6.6$ that consists of three
separated UV-continuum components. Our observations reveal several
well-separated components of CII emission. The two most luminous components
in CII coincide with the brightest UV components (A and B), blue-shifted by
$150$ km s$^-1$ with respect to the peak of Ly$\alpha$ emission.
Other CII components are observed close to UV clumps B and C and are
blue-shifted by $\approx300$ and $\approx80$ km s$^-1$ with respect to the
systemic redshift. We do not detect FIR continuum emission due to dust with a
3$\sigma$ limiting luminosity L$_IR (T_d = 35 \, K) <
3.1\times10^10$ L$_ødot$. This allows us to mitigate uncertainties in the
dust-corrected SFR and derive SFRs for the three UV clumps A, B and C of 29, 6
and 7 M$_ødot$ yr$^-1$. All clumps have CII luminosities consistent
within the scatter observed in the local relation between SFR and L$_\rm
CII$, implying that strong Ly$\alpha$ emission does not necessarily
anti-correlate with CII luminosity. Combining our measurements with the
literature, we show that galaxies with blue UV slopes have weaker CII
emission at fixed SFR, potentially due to their lower metallicities and/or
higher photoionisation. Comparison with hydrodynamical simulations suggests
that CR7's clumps have metallicities of $0.1<Z/Z_ødot<0.2$. The observed
ISM structure of CR7 indicates that we are likely witnessing the build up of a
central galaxy in the early Universe through complex accretion of satellites.
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